I've encountered a lot of code where a variable is compared to a constant.
For example, variable == "value".
This frequently results in issues when the variable is not of the correct type or is null. As a remedy, always compare a constant to a variable.
For instance, "value" == variable, "value".equals(variable).
This way, even if the variable is unassigned or null, it will still return false by default because it is being compared to a constant and will most likely not change.
This appears to be a little and clear distinction, but I have encountered a lot of code where the former is more commonly used than the latter.